Monday, July 18, 2005

Plug-in Hybrids

The problems with gasoline-powered vehicles are that 1) they burn foreign-oil-based gasoline, and lots of it, and 2) they spew nasty stuff out of their tailpipes. The problems with electric vehicles are 1) a lot of heavy batteries are needed to give them a decent range, 2) the electricity to charge the batteries has to come from somewhere, such as coal, oil, gas or nuclear power plants (or--solar or wind!), and 3) good batteries are very expensive.

Matthew Parris pointed out last year that the real key is energy density--gasoline is more than 100 times as energy-dense as are lead-acid batteries. These are the most affordable kind of battery, used to start your car and what I'll be using to store my solar energy. The batteries I have ordered weigh a total of about 1000 pounds, and when charged will store enough energy to power my house for three to five days if I ran them all the way down (which I won't). Based on Parris' numbers, if I had 1000 pounds of gasoline stored at my house and a generator, I would be able to power my house for over a year! Of course, I can't recharge gasoline, and weight isn't a big concern for my basement floor. But weight is crucial in cars (and much more so in airplanes), and the weight of batteries is the main reason that there are very few electric vehicles on the road. Some types of batteries, like lithium-ion and nickel-cadmium, have higher energy densities, but at much higher cost.

This is where the concept of the plug-in hybrid electic vehicle (PHEV) comes in. Combining the cleanliness and the possibility of using renewable energy sources (or at least cheap off-peak electicity) of an electric with the extended range of a gasoline engine, some prototype PHEV's are now getting 144 mpg (that gallon of gas is boosted by 7 kWh of electricity--68 cents worth at current prices).

For lots more info on PHEV's and their controversial future, see this article from the LA Times or the latest issue of Home Power magazine. (They used to have the latest issue available for free download, but now it costs $5. It appears you can also wait a couple of months and download the August/September issue for free then--the June/July issue is available free now. If you've never seen Home Power and have a high-speed connection, you might enjoy downloading it.)

I've been thinking that my biodiesel-powered VW might be the last car I ever buy, but I can see a PHEV working very nicely as a dump load for my solar roof. PHEV's also will supposedly function very nicely as generators when needed, meaning I might be able to go completely off-grid, running my house AND my car on solar along with just a few gallons of gasoline (or biodiesel?) a year. The current PHEV conversions are all based on the Toyota Prius, but there's no reason that a (bio-)diesel-powered PHEV couldn't be made. The key to widespread acceptance of PHEV's, according to both articles, is low-cost lightweight batteries, which may be three to five years away.